The present invention relates to a semiconductor device such as a light emitting diode, a laser diode or the like used in optoelectronics or the like.
FIG. 11 is a schematic section view of a first example of a conventional semiconductor device.
This semiconductor device uses a GaAs substrate 10 of III-V semiconductors reported in, for example, "Extended Abstract of Conference on Solid State Devices and Materials (1990)", pages 621 to 624. An n-ZnSSe epitaxial cladding layer 12 is formed on the GaAs substrate 10. Alternately laminated on the n-ZnSSe epitaxial cladding layer 12 are a plurality of n-ZnSSe epitaxial layers 13 and a plurality of n-ZnSe epitaxial layers 14. A p-ZnSSe epitaxial cladding layer 15 is formed on the uppermost n-ZnSSe epitaxial layer 13. Resistive metallic electrodes 16, 17 are respectively formed above the p-ZnSSe epitaxial cladding layer 15 and below the GaAs substrate 10.
In the semiconductor device having the arrangement above-mentioned, the band gap in the n-ZnSSe epitaxial layer 13 is greater than that in the n-ZnSe epitaxial layer 14, the difference in conduction band energy between the layers 13, 14 is as small as about 50 meV or less and the difference in value band energy between the layers 13, 14 is substantially equal to the difference in band gap energy. Accordingly, holes are efficiently confined in a multilayer structure of ZnSSe/ZnSe and recombined with electrons entering this multilayer structure, thus emitting blue light.
FIG. 12 is a schematic section view of a second example of the conventional semiconductor device.
This semiconductor device uses a GaAs substrate 101 of III-V semiconductors reported in, for example, "Applied Physics Letters (1990)" Volume 57, No. 23, pages 2413 to 2415. An n-ZnSe epitaxial cladding layer 22 is formed on the InGaAs substrate 101. Alternately laminated on the n-ZnSe epitaxial cladding layer 22 are a plurality of n-ZnSe epitaxial layers 23 and a plurality of n-ZnCdSe epitaxial layers 24. A p-ZnSe epitaxial cladding layer 25 is formed on the uppermost n-ZnSe epitaxial layer 23. Resistive metallic electrodes 16, 17 are respectively formed above the p-ZnSe epitaxial cladding layer 25 and below the InGaAs substrate 101.
In the semiconductor device having the arrangement mentioned above, the band gap in the n-ZnSe epitaxial layer 23 is greater than that in the n-ZnCdSe epitaxial layer 24, the difference in value band energy between the layers 23, 24 is as small as about 50 meV or less and the difference in conduction band energy between the layers 23, 24 is substantially equal to the difference in band gap energy. Accordingly, electrons are efficiently confined in a multilayer structure of ZnSe/ZnCdSe and recombined with holes entering this multilayer structure, thus emitting light from green to blue.
In the conventional semiconductor device in FIG. 11, the holes can be confined in the multilayer structure, but the electron cannot be confined satisfactorily due to small conduction band offset.
In the conventional semiconductor device in FIG. 12, the electrons can be confined in the multilayer structure, but the holes cannot be confined satisfactorily due to small value band offset.
Thus, either only one of the electrons or holes can be efficiently confined in the multilayer structure. This lowers the carrier in recombination probability, resulting in a decrease in internal quantum efficiency.
To enhance the carrier recombination probability to increase the internal quantum efficiency, it is desired to provide a semiconductor device having such an arrangement that both electrons and holes can be efficiently confined in the multilayer structure, i.e., an arrangement in which both conduction band offset and value band offset are sufficient.